Automatic door-opening system using an acoustic object detection system

ABSTRACT

An object detection system is disclosed which makes use of an acoustic transducer for generating compressional waves in the air and detecting return pulses from an object lying within the detection zone. A transducer mounting system includes a transducer slug mounted for generating acoustic waves from both ends of the slug. The antenna system includes a reflector housing adapted to accommodate variable surfaces for controlling the energy pattern. Details of the electronic circuitry associated with the transducer mounting system and a door opening system are disclosed.

United States Patent Leyde et al.

[ June 26, 1973 AUTOMATIC DOOR-OPENING SYSTEM USING AN ACOUSTIC OBJECTDETECTION SYSTEM Inventors: Warren L. Leyde; Delbert E.

Marker, both of Seattle, Wash.

Republic Industries, Inc., Chicago, 111.

Filed: Sept. 30, 1971 Appl. No.: 185,073

Assignee:

[52] US. Cl. 340/1 R, 49/25, 49/31, 340/16 C [51] Int. Cl. G01s 9/66[58] Field of Search 49/25, 31; 340/1 R, 340/261,1T,16 C

[56] References Cited UNITED STATES PATENTS 3,474,400 10/1969 Auer eta1. 340/1 R fbwreazzsp osmurae 1,929,273 10/1933 Crago 1. 49/253,373,526 3/1968 Parkin..... 340/16 C 3,176,266 3/1965 Auer,.1r. 340/1 RPrimary ExaminerRichard A. Farley Attorney-Christensen & Sanborn [57]ABSTRACT An object detection system is disclosed which makes use of anacoustic transducer for generating compres sional waves in the air anddetecting return pulses from an object lying within the detection zone.A transducer mounting system includes a transducer slug mounted forgenerating acoustic waves from both ends of the slug. The antenna systemincludes a reflector housing adapted to accommodate variable surfacesfor controlling the energy pattern. Details of the electronic circuitryassociated with the transducer mounting system and a door opening systemare disclosed.

7 Claims, 11 Drawing Figures PATENIEU JUNZG I973 SHEET 3 0F 4 AUTOMATICDOOR-OPENING SYSTEM USING AN ACOUSTIC OBJECT DETECTION SYSTEM FIELD OFTHE INVENTION This invention relates to control systems for the openingand closing of doors, and, more particularly, to such systems detectingthe presence of objects within the vicinity of the door by use of anacoustic object detection system.

BACKGROUND OF THE INVENTION Object detection systems of the acousticpulse-echo type have been known and used for some time, espe cially intraffic detection and control systems. Generally, such systems include asource of ultrasonic energy, an ultrasonic transducer coupled to thesource for emitting a narrow pulse or series of pulses of ultrasonicenergy, a second ultrasonic transducer for receiving return pulses fromobjects within a predetermined detection zone, and a detection circuitcoupled to the ultrasonic transducer for providing an output signal whena predetermined criterion is met by return pulses.

The present invention comprises an improvement in systems of this typewhich has particular applicability to door-opening and closing systems,whether used indoors or outdoors.

It is another object of this invention to provide an acoustic objectdetection system which is particularly reliable in outdoor applications.

It is a further object of this invention to provide such an objectdetection system which includes the capability to distinguish betweenvalid pulse returns and invalid pulse returns, such as might be causedby ground, wall, and precipitation surfaces.

It is yet another object of this invention to provide an objectdetection system which is particularly adaptable to the automaticopening and closing of doors.

It is still another object of this invention to provide an antennasystem for an object detection system wherein means are provided tominimize unwanted pulse returns from the antenna system itself.

It is yet a further object of this invention to provide an antennasystem for an object detection system in which control readily can bemade of the beam pattern thereof.

SUMMARY OF THE INVENTION These objects and others are achieved, briefly,by providing a system including an ultrasonic transducer meanstransmitting a pulse or pulses of ultrasonic energy within a detectionzone immediately adjacent a door to be controlled, means receivingacoustic signals including return pulses from objects within thedetection zone, a logic circuit comparing said acoustic signals with apredetermined criterion of said return pulses to be expected when anobject is within the detection zone of the system, and means responsiveto the operation of said logic circuit for controlling the operation ofsaid doors.

BRIEF DESCRIPTION OF THE DRAWINGS The invention can perhaps best beunderstood by reference to the following portion of the specification,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a pictorial view showing a typical installation of two antennasystems for permitting bidirectional control of a door or doors;

FIG. 2 is a cut-away, pictorial view of one embodiment of the antennasystem of this invention;

FIG. 3 is a back, sectional view of the antenna system of FIG. 2;

FIG. 4 is a side, sectional view of the antenna system of FIG. 2;

FIGS. 5 and 6 are additional back-sectional views of the antenna systemshowing alternate embodiments of the side inserts shown in FIG. 3;

FIGS. 7 and 8 are cross-sectional views of additional alternateembodiments of these side inserts;

FIG. 9 is a block diagram of the electronic circuitry of the objectdetection system;

FIG. 10 is a timing diagram illustrating a typical cycle of operationthereof; and

FIG. 11 is a graph illustrating a relationship between return pulsesfrom precipitation and distance thereof from a transmitting transducer.

DESCRIPTION OF A PREFERRED EMBODIMENT With reference now to FIG. 1, awall surface 10 includes doors 12 and 16. Passage through the door 12 ismade in the direction of an arrow 14 and is controlled by a firstacoustic object detection system in cluding an antenna system 20Apositioned on wall 10 so as to sense the presence of individualsdesiring to pass in the direction 14. similarly, passage through thedoor 16 in the direction of an arrow 18 is controlled by a secondacoustic object detection system including an antenna system 203 locatedon wall 10 so as to sense the presence of individuals desiring to passin the direction 18.

It can be readily appreciated that acoustic object detection systemsencounter many difficulties in applications such as illustrated inFIG. 1. For example, false return pulses can be provided by thereflector housing of the antenna system, by the wall surface 10, byeither of the doors 12 or 16, by the floor, railings and other adjacentobjects, and so forth. If the acoustic object detection system is usedoutdoors, false return pulses can also be obtained from the surfaces ofprecipitation.

Therefore, the system must compensate for false returns to the extentthat they do not mask desired returns from individuals or other objectswithin a predetermined detection zone. The embodiment of the antennasystem illustrated in FIGS. 2-4 minimizes ringing of the reflectorhousing thereof and additionally allows variable control of the antennasbeam pattern so as to sharply define the desired detection zone, therebyfurther reducing false returns.

In more detail, the antenna system includes a reflector housing 22 ofmetallic material which preferably has a rough finish on all surfacesthereof. In one embodiment, the material comprised an aluminum alloy.The upper end of the reflector housing 22 is closed and the sidesthereof are flared therefrom to define an interior cavity. The lowerends of the housing sides additionally define a substantiallyrectangular aperture for the transmission and reception of ultrasonicpulses. The narrower sides of the reflector housing 22 include recessedportions 22a, 22b which are flared at a greater angle than are thecorresponding sides.

As a result, the interior cavity of the housing 22 is de fined by leftand right, gradually-tapered surfaces 26b,

26b, by adjoining sharply-tapered surfaces 26a 26a, and by front andback, gradually-tapered surfaces 24a, and 24b. Energy absorbing inserts28, 29 are affixed to surfaces 24b and 24a, and beam-directing inserts30, 31 are affixed to surfaces 26a, 26a. A transducer assembly 32extends downwardly into the cavity and is supported in a manner to bedescribed in more detail hereinafter.

With particular reference now to FIGS. 3-4, the reflector housing 22 isshown in back-sectional and sidesectional views, respectively. In theseviews, the beamdirecting inserts 30, 31 have been replaced by longerembodiments thereof, 30', 31, but otherwise the device is identical tothat shown in FIG. 2. The transducer assembly 32 includes a ceramic slug40 having left and right end surfaces 40a, 40b, respectively. In apractical embodiment, a lead zirconate ceramic was used. As can be seen,ceramic slug 40 is mounted in such a manner by the transducer assembly32 so that transmission occurs simultaneously in opposite directions T1,T2. By this arrangement, the necessity for an energy-absorbing means atone end of the ceramic slug is eliminated. In addition, the power outputof the transducer is practically doubled by virtue of the increasedradiating surface.

Since the ultrasonic radiation occurs substantially in a directionnormal to the plane of the surfaces 40a, 40b, it first comes intocontact with the beam-directing inserts 31', 30'. The surfaceconfiguration of these inserts and their relative orientation withrespect to the directions T1, T2, largely determine the beam pattern ofthe antenna system. Therefore, choice of these inserts allows control ofthe system's detection zone. Additional embodiments 31" and 31 are shownin FIGS. and 6, respectively.

As noted in FIGS. 7 and 8, the configuration of the beam-directinginserts may also be varied in crosssection so as to vary the relativestrength of the beam in planes parallel to the surfaces 40a, 40b of theceramic slug 40.

The beam-directing inserts are preferably composed of a plastic materialhaving a smooth surface presented to the interior cavity. In assembly,the beam-directing inserts are positioned within the cavity adjacentinner surfaces 26a, 26a. Fine tuning is then accomplished by adjustmentof fasteners 33, 34, which are threaded through corresponding aperturesin housing 22 into each beam-directing insert. When tuning isaccomplsihed, the inserts are then maintained in place by an adhesive.

As will be readily recognized by those skilled in the art, thebeam-directing inserts function in a similar manner to direct returns ofthe transmitted pulses back to the surfaces 40a, 40b.

In order to minimize ringing of the antenna system itself, the designthereof must compensate for the fact that ceramic slugs commonly usedhave a narrow bandwidth and a high Q. The application of an ultrasonicpulse thereto causes an oxcillation therein which, if left undamped,would persist for a time sufficient to mask some returns from desiredobjects within the detection area. In addition, returns arising frompulse transmission from the ceramic slug 40 through the transducerarrangement 32 to the housing 22 and back must be minimized, as mustthose pulses returning through the air from the housing 22.

In order to damp the slug oscillations, the sluh 40 is wrapped with aninner layer 42a of neoprene, and an outer layer 4211 of corprene. Layer42a functions primarily to dampen the slug oscillations, whereas layer42b functions primarily to isolate these oscillations from the housing22. In order to achieve the proper amount of damping, the slug 40 isclamped by a nylon clamp 44. The circumferential compression forceexerted on slug 40, and thus the amount of damping, is adjusted by meansof a fastener 46 passing through both legs of clamp 44. In order tocomplete the isolation of the slug 40 from the housing 22, the clamp 44is in turn covered with separate portions 48a, 48b, of

V corp re ne. This assembly is then secured to the housing 22 by atleast one nylon strap 50 whose ends terminate in adjustable tensioningfasteners 51, 52 mounted in the upper surface of housing 22. Electricalconnections are made from the ceramic slug 40 to appropriate terminalpoints in a cavity 53 and connections thereafter made to the remainderof the-system by a cable not illustrated. The cavity 53 may be filledwith a suitable potting compound and enclosed by a cover plate 54.

To minimize ringing of the housing 22 itself, the energy absorbinginserts 28 and 29 are provided. Preferably, these inserts are composedof a plastic material having a relatively rough finish and are securedto the inner surfaces 24b, 24a, by a suitable adhesive.

The antenna system including reflector housing 22 is mounted to anappropriate fixed surface, such as wall 10 in FIG. 1, by a splurality ofnylon fasteners 56 which serve to electrically isolate the mountingsurface and the housing 22 so as to further minimize false returns.

Electronic circuitry of the acoustic object detection system suitablefor use in a door opening system is seen in FIG. 9. Reference shouldalso be made throughout the ensuing discussion to the timing diagram ofFIG. 10. In the embodiment of FIG. 9, timing pulses are provided by aclock source 100. For example, these pulses may be derived from acommonly-available 60 Hz source 102 and comprise pulses having a widthof one millisecond which occur at a repetition rate of 15 Hz. To avoidinterference between adjacent systems, the clock pulses in one systemmay be phase-shifted from those in a second system.

The clock pulses from clock source are applied in turn to a controlledoscillator 104, to a range gate circuit 142, and to a latching thresholddetector 144. Controlled oscillator 104 comprises a standard oscillatorand driver stage operable to provide an output pulse of electricalenergy in the ultrasonic frequency range for the duration of the inputclock pulse thereto. ln a practical embodiment, the frequency ofoscillator 104 was 75 KHz.

The pulse of electrical energy in the ultrasonic frequency range isapplied through a first portion of a duplex circuit including a firstpair of reverse-parallel diodes 106, capacitor 108, a second pair ofreverseparallel diodes 110, and a shielded, RF cable 112 to ceramic slug40. The transmitting pulse is blocked from the remainder of theelectronic circuitry by a second portion of the duplex circuit includinga capacitor 114 and a third pair of reverse-parallel diodes 116, both ofwhich are coupled from the common junction of the signal lead of RFcable 112 and diodes to a source of reference potential.

Shortly after the termination of the transmitting pulse, return pulsesare detected by the ceramic slug 40 and coupled by RF cable 112 to thecommon junction of the duplex circuit. At this time, the duplex circuitacts to couple signals corresponding to the return pulses directly tothe input of an amplifier 120 through capacitor 114 and a capacitor 118.

The return pulses generally comprise four types. First, return pulsesfrom the reflector housing 22 and its elements. These ringing pulsescannot be eliminated because of the proximity of the housing 22 to theceramic slug 40, but can be minimized and controlled by use of theantenna design previously discussed. In most cases, the ringing pulsefrom the housing 22 will have a longer duration than that of thetransmitting pulse of ultrasonic energy, due to ringing of the housing.Second, return pulses from the body of any individual within thedetection zone. These pulses will arrive at the ceramic slug 40 at sometime after the first or housing return pulse because of thecorresponding greater distance between the individual and the slug 40.These pulses will be formed by reflections from the head and shouldersurfaces, then other, lower surfaces of the body and will comprise arelatively highamplitude, short-duration pulse. In a door-openingsystem, these return pulses represent the desired object to be detected.The relative time occurrence of these return pulses will vary withrespect to that of the transmitting pulse of ultrasonic energy, due todifferences in the height and physical characteristics of individuals.Other objects within the detection zone will also cause large returnpulses in this time period.

Third, a return pulse corresponding to a reflection from the floor. Thisreturn pulse will arrive after the housing and body return pulses. Therelative time occurrence of this pulse with respect to the pulse ofultrasonic energy is substantially constant.

Fourth, miscellaneous pulses, which may be characterized as noise. Assuch, they may comprise either reflections of the transmitted pulse fromthe ceramic slug 40, or signals arising from other sources within orwithout the detection zone. A special case of noise comprises thosereflections from precipitation, such as from rain droplets.

Noise signals having a different frequency than that of oscillator 104are discriminated against by tuning amplifier 120 by a circuit 122connected from the voltage source V, to the output terminal thereof. Theoutput signal is then coupled through an automatic gain circuit 124 anda second amplifier 126, which is tuned by a second circuit 128, and acapacitor 129 to the input of a rectifying and level-shifting circuit130. The signal occurring on the output terminal 132 of circuit 130,comprises a rectified version of the four types of return pulsesheretofore mentioned.

Because the noise" return pulses are random, they must be normalizedprior to further signal treatment. Therefore, the system includes afeedback connection from terminal 132 to the control input of automaticgain control circuit 124 which comprises an integrator includinga-series-connected resistor 134 and operational amplifier 136, and acapacitor 138 connected in feedback around operational amplifier 136.

The combination of the integrator in the feedback connection and theautomatic gain control circuit 124 functions as a noise automatic gaincontrol and as a sensitivity time control. First, the integrator isdesigned to have a time constant longer than the expected duration ofthe body return pulses. In this manner, signals corresponding to thesereturn pulses do not affect the operation of the automatic gain control.Second, as the noise" return pulses are generally continuous, thecombination averages out long-term differences therein so as to hold theenvelope of the noise return pulses at a substantially constant level.

Third, the combination serves to discriminate against rain return pulsesin a unique manner. With particular reference now back to FIG. 10, asignal corresponding to the housing return pulse acts to substantiallylower the gain of the system at time T inasmuch as the housing returnpulse is of extended duration greater than the time constant of theintegrator and inasmuch as the magnitude thereof is relatively large.Thegain gradually increases thereafter. With particular reference now toFIG. 1, it has been found that the amplitude of the rain return pulsesdiminshes as the inverse of the distance of the droplets from theceramic slug 40. Therefore, the magnitude of the rain" return pulses isgreatest for droplets immediately adjacent the housing 22. However, itis at this distance, or at the corresponding time t,,, that theattenuation of the automatic gain control circuit 124, in response tothe large housing" return pulse, is greatest. At time t the re turns aremuch weaker but the gain of the system has been increased. Therefore,the rain return pulses are also averaged so that the resultant noisesignal is substantially equivalent to the average noise return pulses.

Therefore, the signals on terminal 132 which correspond to the fourtypes of return pulses, as modified, appear as shown in FIG. 10. Thesesignals are applied to the input of a normally-open switch circuit 140whose output is coupled to the latching threshold detector 144 and whichis controlled by the range gate circuit 142. The control signal fromrange gate circuit 142 is seen in FIG. 10 and begins at a firstpredetermined time t after the production at t of the clock pulse fromclock source and terminates at a second predetermined time t thereafter.The times r are chosen to block signals corresponding to the housing"and floor return pulses.

The latching threshold detector 144 is normally reset at the beginningto each cycle of operation by the clock pulse from clock source 100. Inthis first state, latching threshold detector provides no output signal.However, when range gate circuit 142 has opened switch 140, latchingthreshold detector 144 is triggered into its second state when themagnitude of the signal presented thereto exceeds a threshold valueV,,,,. The valve of V is chosen to be greater than the average value ofthe signals corresponding to the noise" and rain return pulses.Therefore, latching threshold detector 144 blocks noise signals from itsoutput for a certain period of time. If an individual or other object isnot within the detection zone, no body" return pulse is provided andtherefore latching threshold detector remains in its first state so thatno output signal is provided throughout the time that switch 140 isopened by the range gate circuit 142.

However, if latching threshold detector 144 is placed into its secondstate by a large return pulse, the signals are coupled to the input of atwmout-of-three logic circuit 146. The choice of a two-out-of-threelogic circuit is predicated on the assumption that an individual orother object within the detection zone will create at least tworelatively-large amplitude return pulses exceeding the threshold level Vduring successive cycles determined by the clock pulses.

Therefore, logic circuit 146 comprises a counter which furnishes anoutput signal for a predetermined period of time when return pulses aredetected during the range gate period for two out of three successivecycles. This output signal is applied to a Triac control circuit 148which is of a standard configuration. in response, Triac control 148provides a control signal to the gate electrode of a Triac 150 which isconnected in series with a door solenoid 152 across a suitablealternating current voltage source. The time period of conduction ofTriac 150, after passage of an individual is, on the order of onesecond, so as to hold the door open to allow passage of the individualtherethrough and so as to prevent oscillation of the door in response tosecondary detections of the individual within the detection zone at thenext and succeeding clock pulses from clock pulse source 100.

While the invention has thus been described in terms of the preferredembodiment, it is to be fully understood by those skilled in the artthat the invention is not limited thereto, but rather is intended to-bebounded only by the limits of the appended claims.

What is claimed is:

l. A system for automatically controlling the operation of one or moredoors, comprising an ultrasonic transducer means for transmitting andreceiving ultrasonic waves within a predetermined detection zone, meanssupporting said transducer means in proximity to a door so thatindividuals desiring to pass through said door first enter saiddetection zone, clock means developing relatively low frequency clockpulses, an ultrasonic source controlled by said clock means to produce aburst of ultrasonic energy for each of said clock pulses, means couplingsaid source to said transducer, a detection circuit also coupled to saidtransducer and providing an output signal representing pulse returnsfrom objects within said detection zone, said detection circuitcomprising an amplifier, an automatic gain control circuit regulatingthe gain of said detection circuit and an integrating means coupled tothe output of said detection circuit for controlling said automatic gaincontrol circuit in response to the magnitude of said output signal, thetime constant of said integrating means being chosen to be longer thanthe expected duration of return pulses from individuals within saiddetection zone, means coupled to said output signal for discriminatingagainst false pulse returns, said disciminating means providing acontrol signal only when said returns are characteristic of an objectwithin said detection zone, and means controlling the opening or closingof said door in response to said control signal.

2. A door-controlling system as recited in claim I, whereinsaiddiscriminating means includes a normallyopened switch having saidoutput signal connected thereto, a range gate circuit controlled by saidclockpulses closing said switch for a predetermined time periodsubsequent to each of said clock pulses to thereby block close-in andfloor return pulses, a logic circuit having connected thereto the outputof said switch, and a source of a threshold signal coupled to said logiccircuit, said logic circuit being operative to provide said controlsignal only if said output signal exceeds said threshold signal on twoout of three successive cycles determined by said clock pulses.

3. A door-controlling system as recited in claim 1, wherein saiddetection circuit comprises means regulating the components of saidoutput signal corresponding to noise at a predetermined, substantiallyconstant level, and wherein said disciminating means includes a sourceof a threshold signal, the magnitude thereof being greater than that ofthe regulated noise components in said output signal, and a thresholddetector coupled to said threshold signal source which is normallyoperative to inhibit said output signal except when the level thereofexceeds that of said source.

4. A door-controlling system as recited in claim 1, wherein said controlmeans comprises an electrical door actuator, a source of power, acontrol device in circuit with said source and said actuator, and meansenergizing said control device for a relatively long period of time inresponse to said control signal.

5. A door-controlling system as recited in claim 4, wherein said controldevice comprises a bidirectional controllable semiconductor.

6. A door-controlling system as recited in claim 1, wherein saidultrasonic transducer means comprises a reflector housing defining aninterior cavity and an aperture for the passage of ultrasonic waves, anda single transducer slug supported within said cavity.

7. A door-controlling system as recited in claim 1, wherein saidultrasonic energy has a frequency of kHz and said clock source has afrequency of 15 Hz.

1. A system for automatically controlling the operation of one or moredoors, comprising an ultrasonic transducer means for transmitting andreceiving ultrasonic waves within a predetermined detection zone, meanssupporting said transducer means in proximity to a door so thatindividuals desiring to pass through said door first enter saiddetection zone, clock means developing relatively low frequency clockpulses, an ultrasonic source controlled by said clock means to produce aburst of ultrasonic energy for each of said clock pulses, means couplingsaid source to said transducer, a detection circuit also coupled to saidtransducer and providing an output signal representing pulse returnsfrom objects within said detection zone, said detection circuitcomprising an amplifier, an automatic gain control circuit regulatingthe gain of said detection circuit and an integrating means coupled tothe output of said detection circuit for controlling said automatic gaincontrol circuit in response to the magnitude of said output signal, thetime constant of said integrating means being chosen to be longer thanthe expected duration of return pulses from individuals within saiddetection zone, means coupled to said output signal for discriminatingagainst false pulse returns, said disciminating means providing acontrol signal only when said returns are characteristic of an objectwithin said detection zone, and means controlling the opening or closingof said door in response to said control signal.
 2. A door-controllingsystem as recited in claim 1, wherein said discriminating means includesa normally-opened switch having said output signal connected thereto, arange gate circuit controlled by said clock pulses closing said switchfor a predetermined time period subsequent to each of said clock pulsesto thereby block close-in and floor return pulses, a logic circuithaving connected thereto the output of said switch, and a source of athreshold signal coupled to said logic circuit, said logic circuit beingoperative to provide said control signal only if said output signalexceeds said threshold signal on two out of three successive cyclesdetermined by said clock pulses.
 3. A door-controlling system as recitedin claim 1, wherein said detection circuit comprises means regulatingthe components of said output signal corresponding to noise at apredetermined, substantially constant level, and wherein saiddisciminating means includes a source of a threshold signal, themagnitude thereof being greater than that of the regulated noisecomponents in said output signal, and a threshold detector coupled tosaid threshold signal source which is normally operative to inhibit saidoutput signal except when the level thereof exceeds that of said source.4. A door-controlling system as recited in claim 1, wherein said controlmeans comprises an electrical door actuator, a source of power, acontrol device in circuit with said source and said actuator, and meansenergizing said control device for a relatively long period of time inresponse to said control signal.
 5. A door-controlling system as recitedin claim 4, wherein said control device comprises a bidirectionalcontrollable semiconductor.
 6. A door-controlling system as recited inclaim 1, wherein said ultrasonic transducer means comprises a reflectorhousing defining an interior cavity and an aperture for the passage ofultrasonic waves, and a single transducer slug supported within saidcavity.
 7. A door-controlling system as recited in claim 1, wherein saidultrasonic energy has a frequency of 75 kHz and said clock source has afrequency of 15 Hz.